1. Field of the Invention
This invention relates to a precessional centrifugal pump, and more specifically, to a precessional centrifugal pump of the type which is adapted to deliver liquid while rotating it by means of an impeller making a precessional movement.
2. Description of the Related Art
The recent attempt to clinically utilize a light and compact centrifugal pump as a blood pump has attracted considerable attention. However, no conventional centrifugal pump can be rendered useful for purposes of this kind merely by diminishing its size since this would involve various problems such as the danger of germs and foreign matter entering it through the bearings and the sealing section as well as hemolysis (the destruction of red blood cells). In order to overcome these problems, a precessional centrifugal pump has been proposed. The impeller (head) of this centrifugal pump is not attached to a rotating shaft but to a rod which makes a precessional movement. The inventor of the present invention made an intense study of this type of centrifugal pump with a view to improving its efficiency and filed an international application on the subject (International Publication No. W086/04962).
The object of the international application was to provide a precessional centrifugal pump which exhibits a high efficiency and which can effectively prevent hemolysis. FIGS. 5 and 6 show a centrifugal pump in accordance with this international application.
As shown in the drawings, a centrifugal pump 9 exhibits a casing 2 having a conical inner configuration and an annular space 3. The casing 2 has a side wall 2a and an opening 2b provided at the apex thereof. Outwardly, the annular space 3 is defined by the side wall 2a of the casing 2, and, inwardly, by a flow guide wall 7 which extends from the center of the circular end face of the casing 2 into the annular space 3.
The annular space 3 is connected through an inlet way 8 to an inlet 10 provided at the center of the circular end face of the casing 2. The inlet way 8 is a spiral flow passage extending through the flow guide wall 7. The annular space 3 is further connected to an outlet 5 which extends tangentially from that section of the side wall 2a of the casing 2 which faces the inlet way 8 (This section expands smoothly on the outside).
An impeller 6 comprising a head 9 and a rod 14 is arranged in the annular space 3 in such a manner as to be able to run therein. The head 9 of the impeller 6 consists of a conical end section 9a and a base section 9b. The impeller 6 extends in the annular space 3 along the side wall 2a of the casing 2 and along the flow guide wall 7. The rod 14 extends through the opening 2b of the casing 2 to the exterior of the annular space 3.
The opening 2b is covered with a sealing membrane 15 made of a flexible material withstanding repeated bending, such as polyurethane or silicone. The sealing membrane 15 is attached to the side wall 2a of the casing 2 as well as to the impeller 6 in a water-tight manner. The rod 14 of the impeller 6, extending out of the annular space 3, is attached to a supporting member 17 through a bearing 18, the supporting member 17, when rotated, causing the impeller 6 to make a precessional movement around the opening 2b. The supporting member 17 is connected to the shaft of a motor (not shown) and is rotated thereby.
With this precessional centrifugal pump turbulence of flow, etc. in the pump chamber can be prevented to a certain degree, with the pumping efficiency being improved to around 40%.
However, the performance of this prior art pump is still less than perfect. Besides, the problem of hemolysis remains.